Parasomnia

Parasomnia is a windigo, and the protagonist/antagonist/primary character of the Source companion work, "Armiger". She was the only ambassador between the Windigo collective and Princess Celestia during the Second Era.

She eventually finds herself in a fledgeling friendship with Fluttershy, though she quickly discovers that friendship, especially kindness, is poisonous to windigos. However, driven by her nascent feelings, she saves Fluttershy during the Saddle Arabian invasion. This action severs her from the windigo "hive mind", making her mortal. In her weakened state, she is seized by Department of Augury officials, who subject her to cruel experiments.

While not explicitly stated, these experiments most likely resulted in her death.